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I've been working on this homework problem for a while now and I can't seem to figure it out.
The problem is as follows:
Prove that for any sets $A$ and $B$, $P(A) \cup P(B) = P(A\cup B)$ then either $A\subseteq B$ or $B\subseteq A$. I'm having trouble understanding what it means to have an equation as one of my hypotheses.
I looked online and I couldn't find anything online, so hopefully this is alright.
Any help would be appreciated